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Old 6th May 2013, 11:15 AM   #1
dadod is online now dadod  Croatia
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Default Simple line buffer

This is simple line buffer with the quite low distortion. I tried to connect it as a diamond buffer but it worked better in this way. I am not sure how it works but in simulation it works. Output impedance is 110ohm and it's good to drive 10kohm or higher loads. Any comments.
dado
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Old 6th May 2013, 11:24 AM   #2
rjm is offline rjm  Japan
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My take on that is your connection makes Q15, Q16 just act as diodes, to bias the output transistors. I'm mystified as for why you'd think this would be better than than standard diamond buffer though.
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Old 6th May 2013, 12:12 PM   #3
dadod is online now dadod  Croatia
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There is very small difference, but my buffer is a bit better.
diamonf buffer 0.000134% THD20k
this buffer 0.000118% THD20k
below diamond buffer and FFT comparison
dado
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Old 6th May 2013, 12:44 PM   #4
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one question may be if human ears/brain may discriminate such a difference and the other will be that you are only a quarter of the way there .

Meaning that simulation results is just an indication ...this buffer and others will be power supply depending, of course pcb depending , and of course properly matched devices depending

There might be some use after constructed and properly debugged .

This sounds like some integrated Pioneer amplifier spec sheet which very clearly says amplifier distortion 0.013% ( for example ) and while the statement is absolutely real in practice the reference is a game of words and refers to the amplifier only ....well the machine is an integrated amplifier and this number is of no practical use since this machine will work together with preamplifier and source selectors so distortion will never make it t this number ...

So yes ...its attractive but incomplete

Kind regards
Sakis
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Old 6th May 2013, 12:45 PM   #5
AndrewT is offline AndrewT  Scotland
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The distortion components of the 3rd, 5th & 7th are all larger than the preceding even harmonic.

Any idea if this will impact on the "niceness" of the sound?
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Old 6th May 2013, 01:57 PM   #6
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Well with distortion components > 120-200 db down at 2v for a discrete buffer ... One would think it would sound quite nice indeed if the performance could be replicated in real life
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Old 6th May 2013, 01:58 PM   #7
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Q a nice idea IMO by the way Dadod.... Thanks for sharing ...
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Old 6th May 2013, 02:18 PM   #8
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by dadod View Post
This is simple line buffer with the quite low distortion. I tried to connect it as a diamond buffer but it worked better in this way. I am not sure how it works but in simulation it works. Output impedance is 110ohm and it's good to drive 10kohm or higher loads. Any comments.
dado
The bootstrapping of the input transistor's C's eliminates their Early effect, and a contribution to non-linearity.
Bootstrapping all 4 transistors should make a real difference: THD is not additive, and removing one of the sources only reduces the level by ~√2, which is more or less in line with what you observe
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Old 6th May 2013, 03:01 PM   #9
dadod is online now dadod  Croatia
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Quote:
Originally Posted by sakis View Post
So yes ...its attractive but incomplete

Kind regards
Sakis
This is going to be output of the gain block, the one with very low distortion and this output buffer should not spoil to much that.
The gain block with no NFB and with distortion on the level of the 1ppm.
dado
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Old 6th May 2013, 08:43 PM   #10
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I've seen a similar thing called a bootstrapped diamond buffer on this forum and it's quite common/popular. However that circuit 'crosses' the input transistor collectors to the opposite output transistor emitter. See post #1 here for example:

output inductor?

From memory, Scott Wurcer used that output stage in his recent discrete opamp design, though I'm about to run out of battery so you'll have to search that yourselves. As I said, a few others have used the same circuit as well.

I'm not sure whether they had a good reason to 'cross' the collectors though. Maybe it's simply that no-one ever thought of your way.
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